their survival (Bliss 1971). This nursing effect has been mostly observed in an
interspecific context. However, we can predict that this may be an important
phenomenon from an intraspecific perspective, as has been proposed in environmental contexts others than alpine ones (Fajardo and McIntire 2011).
Pseudoviviparity consists of the formation of vegetative diaspores in inflorescences, with the already developed flower parts undergoing proliferation and
transformation into leaf-like structures (Pijl 1972). Species with pseudovivipary are
mostly found in arctic, alpine and arid environments. In the local high-altitude
floras, the proportion of pseudoviviparous species reaches 10% and, in exceptional
cases, even up to 25% (Sarapul’tsev 2001). These habitats may favour pseudovivipary because they are extraordinarily coarse-grained for seedling establishment and the probability of an offspring being dispersed to a suitable patch is very
low. The success of pseudovivipary may also be related to the problems of
establishment and growth in the short, cold growing seasons of these regions (Lee
and Harmer 1980; Elmqvist and Cox 1996). Furthermore, parental care is not
restricted to seedling establishment, as the survival of daughter ramets may be
greatly enhanced by translocation of resources from the parental plant through the
vascular connections. This extended parental care depends on the degree of
physiological integration or independence and is prolonged in the case of ‘extensive
integrators’ (Callaghan 1984; Jónsdóttir 2011). As a rather general trend, parental
care to seeds is substituted by parental care to daughter ramets, which are much
more costly to produce but exhibit much higher survival. Seedling survival is
probably the most critical stage in the life histories of long-lived perennial alpine
plants, determining species’ distribution and range shifts (Kitajima and Fenner
2000).
Seed weight should be affected by altitude because heavier seeds are more likely
to produce larger seedlings that successfully establish in harsh conditions (Westoby
et al. 1992), which is in accordance with the ‘stress-tolerance’ hypothesis (survival
depends on plant stress resistance). However, despite the fact that elevation gradients in seed mass have repeatedly been reported (Baker 1972; Blionis and Vokou
2005), findings were often conflicting and had not revealed any consistent pattern
thus far. Although an increase in seed mass with elevation was reported by Pluess
et al. (2005), there is also evidence of negative relationships between seed mass and
elevation supporting the ‘energy constraints’ hypothesis, which states that lower
temperatures and shorter growing seasons at higher elevations may reduce resource
acquisition and the energy available for seed development and seed provisioning
(Baker 1972; Körner 2003; Bu et al. 2007). Additionally, seed size is subjected to
allometric constraints and thus determined by plant size variation with altitude.
In detail, Pluess et al. (2005) tested the hypotheses that between related
species-pairs and among populations of single species a similar trend for increasing
seed weight with increasing altitude should be present. These authors determined
seed weights from 29 species-pairs, with each pair consisting of one species
occurring in a lowland area and a congeneric species from a high altitude area.
Compared to the related lowland species, 55% of the alpine species had heavier
seeds, 3% (one species) had lighter seeds and 41% had seeds of approximately
268
P. Laiolo and J.R. Obeso
interspecific context. However, we can predict that this may be an important
phenomenon from an intraspecific perspective, as has been proposed in environmental contexts others than alpine ones (Fajardo and McIntire 2011).
Pseudoviviparity consists of the formation of vegetative diaspores in inflorescences, with the already developed flower parts undergoing proliferation and
transformation into leaf-like structures (Pijl 1972). Species with pseudovivipary are
mostly found in arctic, alpine and arid environments. In the local high-altitude
floras, the proportion of pseudoviviparous species reaches 10% and, in exceptional
cases, even up to 25% (Sarapul’tsev 2001). These habitats may favour pseudovivipary because they are extraordinarily coarse-grained for seedling establishment and the probability of an offspring being dispersed to a suitable patch is very
low. The success of pseudovivipary may also be related to the problems of
establishment and growth in the short, cold growing seasons of these regions (Lee
and Harmer 1980; Elmqvist and Cox 1996). Furthermore, parental care is not
restricted to seedling establishment, as the survival of daughter ramets may be
greatly enhanced by translocation of resources from the parental plant through the
vascular connections. This extended parental care depends on the degree of
physiological integration or independence and is prolonged in the case of ‘extensive
integrators’ (Callaghan 1984; Jónsdóttir 2011). As a rather general trend, parental
care to seeds is substituted by parental care to daughter ramets, which are much
more costly to produce but exhibit much higher survival. Seedling survival is
probably the most critical stage in the life histories of long-lived perennial alpine
plants, determining species’ distribution and range shifts (Kitajima and Fenner
2000).
Seed weight should be affected by altitude because heavier seeds are more likely
to produce larger seedlings that successfully establish in harsh conditions (Westoby
et al. 1992), which is in accordance with the ‘stress-tolerance’ hypothesis (survival
depends on plant stress resistance). However, despite the fact that elevation gradients in seed mass have repeatedly been reported (Baker 1972; Blionis and Vokou
2005), findings were often conflicting and had not revealed any consistent pattern
thus far. Although an increase in seed mass with elevation was reported by Pluess
et al. (2005), there is also evidence of negative relationships between seed mass and
elevation supporting the ‘energy constraints’ hypothesis, which states that lower
temperatures and shorter growing seasons at higher elevations may reduce resource
acquisition and the energy available for seed development and seed provisioning
(Baker 1972; Körner 2003; Bu et al. 2007). Additionally, seed size is subjected to
allometric constraints and thus determined by plant size variation with altitude.
In detail, Pluess et al. (2005) tested the hypotheses that between related
species-pairs and among populations of single species a similar trend for increasing
seed weight with increasing altitude should be present. These authors determined
seed weights from 29 species-pairs, with each pair consisting of one species
occurring in a lowland area and a congeneric species from a high altitude area.
Compared to the related lowland species, 55% of the alpine species had heavier
seeds, 3% (one species) had lighter seeds and 41% had seeds of approximately
268
P. Laiolo and J.R. Obeso